<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>居中总结</title>
  <style>
  .container {
    height: 300px;
    background-color: lightblue;
  }
  .container .content {
    width: 300px;
    height: 200px;
    background-color: lightcoral;
  }
  </style>
</head>
<body>
  
  <div class="container">
    <div class="content"></div>
  </div>
</body>
</html>